Lighting systems are becoming increasingly intelligent to respond to a growing demand for personalization, efficiency and simplicity. In recent years lighting devices have been developed to address these demands. For example, the lighting device called LumiMotion, manufactured by Philips, includes a camera and a processing unit to detect the presence of a person close to the lighting device, and temporarily turn on the lighting device or increase its light output. When it is not trigged the lighting device is dimmed or fully turned off. Another example is a so called tuneable white lighting device, which enhances the look of illuminated products. The lighting device is arranged to determine appropriate settings by analyzing the colors of the illuminated products by means of image processing using an embedded camera and a processing unit. The appropriate settings are automatically chosen by the lighting device.
Thus, in general terms, lighting devices having sensing capabilities as described above, are designed to adapt their light output depending on the scene and situation they are observing. In order to infer accurate information about the scene and the influence of the lighting device itself, a calibration step is typically required. Relevant information to be acquired during the calibration can be for instance; spatial footprint of the light, amount and type of light provided in different parts of the scene, ambient illumination, scene layout and appearance, etc. In order to obtain this kind of information, different calibration strategies can be designed, but they are typically based on capturing one image of the scene with the light output of the lighting device turned off, and one image with the light output set to a predetermined value. However, there is a problem of changes in the scene during the calibration, e.g. caused by other nearby lighting devices carrying out calibration at the same time. As regards the impact of other lighting devices, it can be eliminated in a centrally controlled lighting system where the central controller calibrates one lighting device at a time with the others off. However, it is desired to provide an independent lighting device executing a self-calibration method which is less sensitive to disturbances in the scene, and which does not require the infrastructure associated with a centrally controlled lighting system.